Human malaria disease is a worldwide disease with estimated 225 million cases, accounting for 800,000 deaths per year. This disease is caused by a parasite protozoan, in which the parasite infects red blood cells of the host and hemozoin biocrystals are disposed as by-products after the ingestion of haemoglobins. Since the malaria disease can aggravate into a fatal illness within hours upon development of the first symptom, the early diagnosis of malaria infection is important, which requires the detection of hemozoin at low concentrations in infected blood cells.
Malaria disease control, including both diagnosis and treatment, has thus become an important global health issue. Since effective drugs for malaria treatment have not been developed, early malaria diagnosis is important in the malaria disease control to curtail morbidity, mortality and transmission of malaria, by prompting early treatment and cure of malaria infection.
In malaria diagnosis, microscopic examination of blood smears remains the “gold standard” for the detection of malaria parasite, but this method is labour-intensive and time-consuming. Moreover, it requires special expertise from operators for reliable data interpretation.
Recently, several other malaria diagnosis techniques, such as the quantitative buffy coat method, molecular diagnostic method, flow cytometry technique, serological tests, and laser desorption mass spectrometry, have been developed to address these shortcomings. Among these methods, Resonance Raman Spectroscopy (RRS) has been reported to amplify the Raman signal of dried β-hematin crystals by the close Raman shift matching of the laser source and electronic transition of β-hematin. It has been found that β-hematin crystals, which are synthetic forms of hemozoin biocrystals, are similar to hemozoin biocrystals in molecular structure and thus have Raman signals equivalent to hemozoin. Hence, improved methods for the detection of β-hematin, may similarly be applied to improve hemozoin detection and thus, since the presence of hemozoin is indicative of malaria infection, malaria diagnosis.
Besides RRS, Surface Enhanced Raman Spectroscopy (SERS) has also been shown to enhance the Raman spectrum of hematin (soluble form of β-hematin) at 1×10−5 M via the augmented electromagnetic coupling between hematin and gold or silver nanoparticles.
Although the above methods show promise in the detection of hemozoin, the presence of hemozoin at low concentrations in the early stages of malaria infection, where in the ring stage for instance the concentration can be less than 1×10−5 M, renders the RRS and SERS methods insufficient for an effective detection of hemozoin in the earlier stage of malaria infection.
Therefore, there remains a need to develop a more sensitive detection technique, which requires minimal labor and expertise for hemozoin detection, particularly in the diagnosis of early stage malaria infection where concentration of hemozoin may be 1×10−5 M or less.